In a relational database, a dependency occurs when information stored in the same database table uniquely determines other information stored in the same table. A multivalued dependency occurs when the presence of one or more rows in a table implies the presence of one or more other rows in the same table. In other words, two attributes (or columns) in a table are independent of each other, but both depend on a third attribute.
07 04 multivalued dependencies part 1
A multivalued dependency avoids the normalization standard fourth normal form. Relational databases follow five normal forms that represent guidelines for record design. They avoid update anomalies and inconsistencies in the data. The fourth normal form deals with many-to-one relationships in a database.
To understand a multivalued dependency, it is useful to review what a functional dependency is.
If a characteristic X uniquely determines a characteristic Y, then Y is functionally dependent on X. This is written as X -> Y. For example, in the Students table below, the Student_Name determines the Major:
